The invention pertains to electromechanical devices having a reciprocally moving member moveable between two limits. A typical structure of this character comprises a striker mechanism for a gong. Devices of this nature may be operated with either ac or dc current. When ac current is used, it is necessary to either design the device to function with the frequency of the available ac current; or to provide an ac current having a frequency adapted to certain characteristics of the mechanism. When the devices are to be used with dc current, it is necessary to provide for intermittent, or interrupted, application of the dc potential to the actuating solenoid. For decades, it has been customary to manufacture bells, buzzers, and gongs wherein the mechanism for interrupting the application of dc power to the actuating solenoid comprises a pair of mechanical contacts which are closed when the device is in its rest position and which are opened in response to the actuation of the reciprocating member. Devices of this nature have a variety of disadvantages including, but not limited to, the following:
(1) The contacts must be capable of interrupting the peak current to the solenoid;
(2) The adjustment of the contacts with respect to when they make and break relative to the motion of the reciprocating member may be critical;
(3) The contacts sometimes pit or burn and become inoperative and/or stick together and fail to open;
(4) The frequency of operation per unit time may be varied only over narrow limits.
In view of these disadvantages of the simple circuit for interrupting current to the actuating solenoid, a wide variety of designs have been proposed to overcome these difficulties. For example, U.S. Pat. No. 3,781,877 issued Dec. 25, 1973 to Berns provides an astable multivibrator for driving the solenoid. U.S. Pat. No. 3,931,549 issued Jan. 6, 1976 to Berns et al discloses a structure requiring two windings on the solenoid and making use of opposing magnetic fluxes. Other U.S. Pat. Nos. such as 4,153,898 issued May 8, 1979 to Larime; 4,136,377 issued Jan. 23, 1979 to Larime; 4,005,413 issued Jan. 25, 1977 to Berns; and 3,656,156 issued Apr. 11, 1972 to Berns disclose a variety of devices of the class first described. All of the cited patents are assigned to the same assignee as the present invention.
Because bells, chimes, gongs, and buzzes are such ubiquitous devices, a wide variety thereof have been designed and manufactured for special and general applications. Many designs have been made the subject of patent applications and many patents disclosing individual features thereof may be found in the art.